Sea Turtles Often Get Lost for Miles, but Always Find Their Destination
By Elizabeth Claire Alberts
When baby sea turtles hatch from their eggs, they skitter across the sand to the shoreline before disappearing into the open ocean. Many years later, by some remarkable feat, female turtles find their way back, sometimes traveling thousands of kilometers, to arrive at the exact beach where they were born. This time, it's to lay their own eggs.
It's believed that turtles use the Earth's geomagnetic field to find their way, but there is still a lot that's unknown about this process. A team of scientists, who published a new paper in Current Biology this month, used satellite tracking to study the navigation skills of female green turtles (Chelonia mydas). They found that while green turtles eventually arrived at their preferred destination, they didn't always get there with pinpoint accuracy, but followed a kind of "crude map."
A green turtle in Martinque. Michelle Roux / Coral Reef Image Bank
"I think we had this idea that turtles were running on rails, and that they had some sort of fine scale navigational ability," Alex Rattray, co-author of the paper and research fellow at the School of Life and Environmental Sciences at Deakin University in Australia, told Mongabay. "But what we found out is that they make mistakes, they miss their targets, they overshoot the targets, and they do a lot of searching."
Nesting grounds aren't the only locations sea turtles habitually return to — they also return to the same foraging grounds. In fact, another study found that migrating sea turtles were so loyal to their preferred foraging locations that they would bypass other suitable places to forage while searching for their "home" site. Green turtles, in particular, demonstrate a very high fidelity to foraging grounds, and do not stop anywhere else during open-ocean crossings, according to the study, which makes the species an ideal subject matter.
The research team collected data by fitting satellite trackers to 35 sea turtles nesting on the island of Diego Garcia in the Indian Ocean. The trackers transmitted high-accuracy Fastloc-GPS location data several times each day. Once the turtles laid their eggs, they returned to the ocean to travel to their foraging grounds off the coasts of small, isolated islands. But most of the time, the turtles did not get there directly, sometimes traveling several hundred kilometers off course before reaching their destination.
"We were also surprised at the distance that some turtles migrated," Graeme Hays, lead author of the study and the Alfred Deakin professor of marine science at Deakin University, said in a statement. "Six tracked turtles travelled more than 4,000 kilometers [2,500 miles] to the east African coast, from Mozambique in the south, to as far north as Somalia. So, these turtles complete round-trip migrations of more than 8,000 kilometers [5,000 miles] to and from their nesting beaches in the Chagos Archipelago."
While the green turtles traveled via circuitous routes, the study showed that they do have the ability to navigate vast swaths of the ocean, and to reorient themselves when astray.
"None of these turtles got irrevocably lost," Rattray said. "They all eventually found a way home. One of the turtles … [traveled off course] about 200 kilometers [120 miles] south of its destination after one month, and then spent another two months finding its way back to its target after it'd overshot it.
Green sea turtle. Greg Asner
"They're amazing creatures," he added, "and they truly are the number one navigators in the world."
Green turtles are an endangered species on the IUCN Red List. Primary threats include fishing net entanglement, habitat degradation, boat strikes, and egg harvesting. However, due to global conservation efforts, green turtle populations appear to be slowly rebounding.
Rattray said the team hopes its findings will help inform efforts to protect larger areas of the ocean, encompassing both the nesting and foraging grounds of sea turtles.
"Diego Garcia is a marine protected area … but they [female green turtles] are only there about 10% of their lives," Rattray said. "The rest of the time, they don't respect national boundaries. So, the conservation future of these turtles relies on the efforts of 12 to 15 governments. There has to be a concerted effort throughout the rest of the turtle's life cycle to protect them in some way."
Reposted with permission from Mongabay.
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When hurricanes and other extreme storms unleash downpours like Tropical Storm Beta has been doing in the South, the floodwater doesn't always stay within the government's flood risk zones.
New research suggests that nearly twice as many properties are at risk from a 100-year flood today than the Federal Emergency Management Agency's flood maps indicate.
Flooding Outside the Zones<p>About <a href="https://furmancenter.org/files/Floodplain_PopulationBrief_12DEC2017.pdf" target="_blank">15 million</a> Americans live in FEMA's current 100-year flood zones. The designation warns them that their properties face a 1% risk of flooding in any given year. They must obtain flood insurance if they want a federally ensured loan – insurance that helps them recover from flooding.</p><p>In Greater Houston, however, <a href="https://doi.org/10.1111/j.1539-6924.2012.01840.x" target="_blank">47% of claims</a> made to FEMA across three decades before Hurricane Harvey were outside of the 100-year flood zones. Harris County, recognizing that FEMA flood maps don't capture the full risk, now <a href="https://www.hcfcd.org/floodinsurance" target="_blank" rel="noopener noreferrer">recommends that every household</a> in Houston and the rest of the county have flood insurance.</p><p>New risk models point to a similar conclusion: Flood risk in these areas outstrips expectations in the current FEMA flood maps.</p><p>One of those models, from the <a href="https://firststreet.org/flood-lab/research/2020-national-flood-risk-assessment-highlights/" target="_blank">First Street Foundation</a>, estimates that the number of properties at risk in a 100-year storm is 1.7 times higher than the FEMA maps suggest. Other <a href="https://doi.org/10.1088/1748-9326/aaac65" target="_blank" rel="noopener noreferrer">researchers</a> find an even higher margin, with 2.6 to 3.1 times more people exposed to serious flooding in a 100-year storm than FEMA estimates.</p>
What FEMA’s Flood Maps Miss<p>Understanding why areas outside the 100-year flood zones are flooding more often than the FEMA maps suggest involves larger social and environmental issues. Three reasons stand out.</p><p>First, some places rely on relatively old FEMA maps that don't account for recent urbanization.</p><p>Urbanization matters because impervious surfaces – think pavement and buildings – are not effective sponges like natural landscapes can be. Moreover, the process for updating floodplain maps is locally variable and can take years to complete. Famously, New York City was updating its maps when Hurricane Sandy hit in 2012 but hadn't finished, meaning flood maps in effect <a href="https://projects.propublica.org/nyc-flood/" target="_blank">were from 1983</a>. FEMA is required to assess whether updates are needed every five years, but the <a href="https://www.fema.gov/cis/nation.html" target="_blank" rel="noopener noreferrer">majority of maps</a> <a href="https://www.oig.dhs.gov/sites/default/files/assets/2017/OIG-17-110-Sep17.pdf" target="_blank" rel="noopener noreferrer">are older</a>.</p><p>Second, binary thinking can lead people to an underaccounting of risk, and that can mean communities fail to take steps that could protect a neighborhood from flooding. The logic goes: if I'm not in the 100-year floodplain, then I'm not at risk. Risk perception <a href="https://doi.org/10.1088/1748-9326/ab195a" target="_blank" rel="noopener noreferrer">research</a> backs this up. FEMA-delineated flood zones are the major factor shaping flood mitigation behaviors.</p><p>Third, the era of climate change scuttles conventional assumptions.</p><p>As the planet warms, extreme storms are becoming <a href="https://nca2018.globalchange.gov/" target="_blank">more common and severe</a>. If greenhouse gas emissions continue to increase at a high rate, computer models suggest that the chances of a severe storm dropping 20 inches of rain on Texas in any given year will increase from about 1% at the end of the last century to 18% at the end of this one, a chance of <a href="https://doi.org/10.1073/pnas.1716222114" target="_blank" rel="noopener noreferrer">once every 5.5 years</a>. So far, <a href="https://www.rstreet.org/wp-content/uploads/2020/02/195.pdf" target="_blank" rel="noopener noreferrer">FEMA hasn't taken into account the impact climate change is having</a> on extreme weather and sea level rise.</p>
Racial Disparities in Flooding Outside the Zones<p>So, who is at risk?</p><p>Years of research and evidence from storms have highlighted social inequalities in areas with a high risk of flooding. But most local governments have less understanding of the social and demographic composition of communities that experience flood impacts outside of flood zones.</p><p>In analyzing the damage from Hurricane Harvey in the Houston area, I found that <a href="https://doi.org/10.1088/1748-9326/aba0fe" target="_blank">Black and Hispanic residents disproportionately experienced flooding</a> in areas beyond FEMA's 100-year flood zones.</p><p>With the majority of flooding from Hurricane Harvey occurring outside of 100-year flood zones, this meant that the overall impact of Harvey was racially unequal too.</p><p>Research into where flooding occurs in Baltimore, Chicago and Phoenix points to some of the potential causes. <a href="https://www.nap.edu/read/25381/chapter/4#16" target="_blank" rel="noopener noreferrer">In Baltimore and Chicago</a>, for example, aging storm and sewer infrastructure, poor construction and insufficient efforts to mitigate flooding are part of the flooding problem in some predominantly Black neighborhoods.</p>
What Can Be Done About It<p>Better accounting for those three reasons could substantively improve risk assessments and help cities prioritize infrastructure improvements and flood mitigation projects in these at-risk neighborhoods.</p><p>For example, First Street Foundation's risk maps account for <a href="https://firststreet.org/flood-lab/research/flood-model-methodology_overview/" target="_blank">climate change</a> and present <a href="https://floodfactor.com/" target="_blank" rel="noopener noreferrer">ratings</a> on a scale from 1 to 10. FEMA, which works with communities to update flood maps, is <a href="https://www.fema.gov/media-library-data/1521054297905-ca85d066dddb84c975b165db653c9049/TMAC_2017_Annual_Report_Final508(v8)_03-12-2018.pdf" target="_blank" rel="noopener noreferrer">exploring rating systems</a>. And the National Academies of Sciences, Engineering and Medicine recently <a href="https://www.nationalacademies.org/news/2019/03/new-report-calls-for-different-approaches-to-predict-and-understand-urban-flooding" target="_blank" rel="noopener noreferrer">called for a new generation of flood maps</a> that takes climate change into account.</p><p>Including recent urbanization in those assessments will matter too, especially in fast-growing cities like Houston, where <a href="https://authors.elsevier.com/a/1boBRyDvMFW6W" target="_blank" rel="noopener noreferrer">386 new square miles</a> of impervious surfaces were created in the last 20 years. That's greater than the land area of New York City. New construction in one area can also <a href="https://scalawagmagazine.org/2018/01/city-in-a-swamp-as-houston-booms-its-flood-problems-are-only-getting-worse/" target="_blank" rel="noopener noreferrer">impact older neighborhoods downhill</a> during a flood, as some Houston communities discovered in Hurricane Harvey.</p><p>Improving risk assessments is needed not just to better prepare communities for major flood events, but also to prevent racial inequalities – in housing and beyond – from <a href="https://www.npr.org/2019/03/05/688786177/how-federal-disaster-money-favors-the-rich" target="_blank" rel="noopener noreferrer">growing</a> after the unequal impacts of disasters.</p>
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